An exhaust gas recirculation (EGR) technique, which recirculates a portion of exhaust gas of an internal combustion engine to an air intake side as EGR gas, is known as a technique that limits generation of nitrogen oxide (NOx) contained in the exhaust gas of the engine.
This EGR technique can reduce the quantity of NOx by increasing the quantity of the EGR gas. However, when the EGR gas is excessively recirculated, the particulate matter (PM) is likely generated. With respect to this point, a technique of reducing NOx has been proposed. According to this technique, a combination of an EGR apparatus in a high pressure system and an EGR apparatus in a low pressure system is used to limit the generation of the particulate matter (PM) and to reduce NOx.
However, the EGR apparatus of the low pressure system recirculates the EGR gas from a region, in which the exhaust gas pressure is relatively low, to a region, in which generation of the intake air negative pressure is relatively low. Therefore, although it is possible to return the small quantity of the EGR gas to the engine, it is difficult to recirculate the large quantity of the EGR gas to the engine.
In order to address such a disadvantage, JP2011-32929A (corresponding to US 2011/0023846A1) proposes a low pressure EGR apparatus, in which an intake air throttle valve 120 is placed in a portion of an intake passage 110, which is located on an upstream side of a merging portion, at which a low pressure EGR passage 100 is merged with the intake passage 110, as shown in FIG. 10. In an operational range of the engine, in which a large quantity of the EGR gas needs to be recirculated into the engine, the opening degree of the intake air throttle valve 120 is controlled such that the intake air throttle valve 120 is driven in a valve closing direction thereof for closing the intake air throttle valve 120, i.e., in a direction for increasing the negative intake air pressure.
Furthermore, in the low pressure EGR apparatus of JP2011-32929A (corresponding to US 2011/0023846A1), an output (output characteristics) of an actuator, which drives a low pressure EGR valve 130, is converted through a link device and is then transmitted to the intake air throttle valve 120. Thereby, a dedicated actuator, which is dedicated to drive the intake air throttle valve 120, is eliminated. Furthermore, JP2011-32929A (corresponding to US 2011/0023846A1) teaches a technique of determining a failure of the intake air throttle valve 120 with use of a rotational angle sensor, which senses a rotational angle of the low pressure EGR valve 130, in order to counteract a case where the intake air throttle valve 120 cannot be controlled due to a malfunction of the link device.
According to the technique of determining the failure of the intake air throttle valve, the rotational angle of the low pressure EGR valve 130 is sensed to determine that the intake air throttle valve 120 is failed in a case where the opening degree of the intake air throttle valve 120 is different from an opening degree, which corresponds to a maximum opening degree that is limited by a mechanical stopper, i.e., a case where a cam place, which is rotated integrally with the low pressure EGR valve 130, is placed outside of a normal operational angular range. However, in the case of the above failure determining technique, the operational angular range of the cam plate is increased. That is, when the link device is failed, the low pressure EGR valve 130, which is urged in a valve closing direction thereof by a spring, is rotated beyond a full close position, at which the opening degree of the low pressure EGR passage 100 is minimum, in a direction opposite from a normal opening direction (an opening direction in a normal operational state where the link device is not failed). Therefore, the cam plate, which is rotated integrally with the low pressure EGR valve 130, is placed outside of the normal operational angular range of the cam plate.
As a result, since the operational angular range of the cam plate is increased, it is necessary to provide an additional operational space to allow the increase in the operational angular range of the cam plate. Thereby, a size of the low pressure EGR apparatus, which includes the link device, is disadvantageously increased.